This invention relates to the use of novel co-catalysts which produce a reduction in the formation of undesirable chlorinated dioxin by-products in the preparation of pentachlorophenol or tetrachlorophenol from phenol or lower chlorinated phenols.
In processes well-known in the art for the chlorination of phenols or partially chlorinated phenols such as pentachlorophenol, the usual practice has been to use such catalysts as aluminum chloride, aluminum, antimony pentachloride and ferric chloride. Subsequent to chlorination, the molten tetrachlorophenol or pentachlorophenol is pumped to heated storage facilities pending flaking, prilling or molding operations which are necessary to change the material to a commercially usable form as finished product. In the case of pentachlorophenol, valuable for its fungicidal activity, the specifications are low alkali insoluble content, low insolubles in alkane solvents and a minimum of 86% pentachlorophenol content.
Prior art relating to the lowering of the amount of undesirable chlorinated dioxins formed in the preparation of pentachlorophenol is U.S. Pat. No. 4,160,114 to Shelton et al, wherein organic sulfides are directly utilized as a co-catalyst along with aluminum chloride to effect this result. The specification of the Shelton et al patent is incorporated by way of reference in this application.
There also exists prior art taught in U.S. Pat. Nos. 3,816,268 and 3,909,364 wherein chlorinated dioxins in pentachlorophenol are elaborately reduced to a lower level by distillation under vacuum using stabilizers to prevent decomposition at the required high temperatures. Although low amounts of dioxins are obtained in the distilled pentachlorophenol, a residue of pot material remains containing extremely high quantities of dioxins.
Undesirable by-products called chlorinated dioxins are present in amounts of from 200 to 8,000 parts per million in pentachlorophenol and in lesser amounts of tetrachlorophenol as manufactured by the classical phenol chlorination methods. The primary undesirable dioxins formed are hexachlorodibenzodioxins, heptachlorodibenzodioxins and octachlorodibenzodioxins.
It has been found that the amount of these chlorinated dioxins in tetrachlorophenol or pentachlorophenol can be reduced by the use of certain elements and compounds formed from these elements which, when used in conjunction with aluminum chlorination catalysts involved in synthesis, were effective in inhibiting the amount of chlorinated dioxins formed. Furthermore, these elements or compounds containing these elements acting as inhibitors for the formation of dioxins can be utilized within existing pentachlorophenol plant systems and equipment without modification or need for new construction. These inhibiting elements in low amounts can be placed within the reaction vessel along with the usual aluminum chlorination catalyst to effect reduction of chlorinated dioxins with little noticeable loss in manufacturing time and with little effort. The co-catalyst-inhibitors are also effective during holding cycles necessary in the manufacturing process. The significantly low amount of chlorinated dioxins produced during the practice of this invention exists only in the highly dispersed or diluted form in the finished product. This reaction in dioxins eliminates the necessity of disposing of highly concentrated dioxins in pot residue that arise from the distillation procedure in prior art, as well as presenting a product that has a substantially reduced dioxin content.
It has been found that certain elements have dioxin-reducing properties and can be utilized either directly in their elemental form or in halogenated or sulfonated form, or as alkyl oxides and mixtures of elements, and such compounds or elements effect the reduction of dioxins in tetrachlorophenol or pentachlorophenol produced by the standard commercial chlorination process.
Exemplary of the elements and compounds formed therefrom found to have appreciable dioxin reduction properties during the chlorination of phenols using known chlorination catalyst are antimony, bismuth, chromium, cobalt, gadolinium, germanium, iridium, magnesium, manganese, niobium, rhenium, rhodium, samarium, zirconium and tin, and the halides, sulfides and lower alkyl oxides formed from these elements or mixturs thereof. These elements or compounds formed therefrom act as co-catalyst inhibitors with the standard known catalyst used in commercial chlorination processes to produce polychlorinated phenols by reducing significantly the formation of chlorinated dioxins which are undesirable by-products.
Typical of the catalysts used in production of chlorinated phenols and with which the co-catalyst inhibitors of this invention have been found to produce excellent chlorinated dioxin reduction results are aluminum chloride, ferric chloride, aluminum tris-butoxide, antimony chloride, stanous chloride and metallic alumina, antimony, copper, tin and mixtures thereof.
It has also been found that the presence of from about 0.0001/moles to about 0.05 moles per mole of phenol or lower chlorinated phenol of a sulfur-containing co-catalyst produces excellent results in the system using the inhibitors of this invention. Typical sulfur-bearing compounds that can be used include sulfur, diphenyl sulfide, diphenyl disulfide, dicresyl disulfide, dihexadecyl sulfide and dibenzothiophenol thiophenol, parachlorothiophenol, para, paradichlorophenyl sulfide, sodium hydrosulfide, 2,2'-thio bis (4,6-dichlorophenol) benzyl disulfide, diisopentyl sulfide, naphthalenethiol, heptyl sulfide and hexachlorophenyl sulfide.
In the manufacture of tetrachlorophenol or pentachlorophenol, the preferable quantity of the co-catalyst inhibitors to be added with the catalyst is from about 0.0001 to about 0.03 moles per mole of phenol or chlorophenol starting materials although it has been found that the use of 0.0001 to 0.5 moles of these inhibitors will produce dioxin-reducing results.
It was found that the novel co-catalyst inhibitors of this invention, when added with aluminum chloride of metallic aluminum catalysts in a phenol chlorination process, produced a pronounced reduction of chlorinated dioxins with reduction in the range of about 4% to about 26%. The following chlorinated dioxin inhibitors and mixtures thereof produced such significant reduction in total chlorinated dioxins:
Antimony pentachloride PA0 Chromium dichloride PA0 Chromium powder PA0 Chromium sulfide PA0 Cobalt metal PA0 Gadolinium trichloride PA0 Germanium tetrachloride PA0 Hafnium tetrachloride PA0 Indium chloride PA0 Magnesium turnings PA0 Manganese dichloride PA0 Niobium chloride PA0 Zirconium tetrachloride PA0 Antimony pentachloride PA0 Antimony powder PA0 Bismuth trichloride PA0 Chromium metal PA0 Cobalt fluoride PA0 Cobalt metal PA0 Hafnium tetrachloride PA0 Iridium chloride PA0 Niobium pentachloride PA0 Rhenium pentachloride PA0 Rhodium chloride PA0 Rubidium trichloride PA0 Samarium trichloride PA0 Tantalum chloride PA0 Tin powder PA0 Tungsten hexachloride PA0 Zinc fluoride PA0 Zirconium tetrachloride
and the following chlorinated dioxin inhibitors produced significant reduction in the more toxic hexachlorodioxins with a reduction of from about 40% to 75%:
While most of the co-catalyst-inhibitors are effective when used with an aluminum chloride catalyst, it has been found that zirconium tetrachloride and/or hafnium tetrachloride can be used as the sole catalyst with the result that chlorinated dioxins are reduced in the chlorinated phenol process.
The practice of this invention is further illustrated by the following examples. It is not intended, however, that this invention be limited by or to the examples.